I learned this breathing practice from Ashtanga teacher John Scott. I've found it very helpful since you can use it almost anywhere and it brings you right in the present moment. I also find it shows that Vinyasa "movement with breath" can be done just with moving your thumb around your hand and therefore almost everyone can do it. Its a great example that yoga is not about doing complicated asanas but just taking time to come into your breath and body.
Heres a short video on how to do the practice.
Below are listed the Sanskrit and then the English after it. Learn the English first then see if you can memorize the Sanskrit numbers.
Puraka means Inhale
Rechaka means Exhale
Start with the thumb of the left hand at the base of the forefinger then move your thumb around just like in the diagram above finishing
Rechaka (Uncounted Exhale)
1. Ekam Puraka - Ekam Rechaka - 1 Inhale - 1 Exhale
2. Dway Puraka - Dway Rechaka - 2 Inhale - 2 Exhale
3. Treeny Puraka - Treeny Rechaka - 3 Inhale - 3 Exhale
4. Chatvari Puraka - Chatvari Rechaka - 4 Inhale - 4 Exhale
5. Panca Puraka - Panca Rechaka - 5 Inhale - 5 Exhale
6. Shat Puraka - Shat Rechaka- 6 Inhale - 6 Exhale
7. Supta Puraka - Supta Rechaka - 7 Inhale - 7 Exhale
8. Astau Puraka - Astau Rechaka - 8 Inhale - 8 Exhale
9. Nava Puraka - Nava Rechaka - 9 Inhale - 9 Exhale
10 Dasha Puraka - Dasha Rechaka - 10 Inhale - 10 Exhale
11. Ekadasha Puraka - Ekadasha Rechaka - 11 Inhale - 11 Exhale
12 Dwadasha Puraka - Dwadasha Rechaka - 12 Inhale - 12 Exhale